[PATCH] tty: serial: fsl_lpuart: potential NULL dereference

[PATCH] tty: serial: fsl_lpuart: potential NULL dereference

[Alexey Khoroshilov]

tty_port_tty_get() might return a tty which is NULL
if the port is not associated with a tty
(e.g. due to close or hangup).
But lpuart_start_rx_dma() dereferences tty without any check.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
---
 drivers/tty/serial/fsl_lpuart.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 76103f2c4a80..9945b37c914a 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -833,9 +833,16 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
 	struct circ_buf *ring = &sport->rx_ring;
 	int ret, nent;
 	int bits, baud;
-	struct tty_struct *tty = tty_port_tty_get(&sport->port.state->port);
-	struct ktermios *termios = &tty->termios;
+	struct tty_struct *tty;
+	struct ktermios *termios;
 
+	tty = tty_port_tty_get(&sport->port.state->port);
+	if (!tty) {
+		dev_err(sport->port.dev, "Port is not associated with a tty\n");
+		return -ENODEV;
+	}
+
+	termios = &tty->termios;
 	baud = tty_get_baud_rate(tty);
 
 	bits = (termios->c_cflag & CSIZE) == CS7 ? 9 : 10;
-- 
2.7.4

Re: [PATCH] tty: serial: fsl_lpuart: potential NULL dereference

[Greg Kroah-Hartman]

On Sat, Dec 10, 2016 at 01:30:36AM +0300, Alexey Khoroshilov wrote:
> tty_port_tty_get() might return a tty which is NULL
> if the port is not associated with a tty
> (e.g. due to close or hangup).
> But lpuart_start_rx_dma() dereferences tty without any check.

Are you sure that tty could ever be NULL here?  This function is only
called in places that seem to have a valid tty, with the maybe exception
of the resume call path.  Can you audit this a bit better to be sure one
way or the other please?

thanks,

greg k-h